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Spring Framework example source code file (ConcurrencyThrottleSupport.java)

This example Spring Framework source code file (ConcurrencyThrottleSupport.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

concurrency, currently, entering, illegalstateexception, illegalstateexception, io, ioexception, no_concurrency, no_concurrency, object, object, serializable, thread, unbounded_concurrency, unbounded_concurrency

The Spring Framework ConcurrencyThrottleSupport.java source code

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Support class for throttling concurrent access to a specific resource.
 *
 * <p>Designed for use as a base class, with the subclass invoking
 * the {@link #beforeAccess()} and {@link #afterAccess()} methods at
 * appropriate points of its workflow. Note that <code>afterAccess
 * should usually be called in a finally block!
 *
 * <p>The default concurrency limit of this support class is -1
 * ("unbounded concurrency"). Subclasses may override this default;
 * check the javadoc of the concrete class that you're using.
 *
 * @author Juergen Hoeller
 * @since 1.2.5
 * @see #setConcurrencyLimit
 * @see #beforeAccess()
 * @see #afterAccess()
 * @see org.springframework.aop.interceptor.ConcurrencyThrottleInterceptor
 * @see java.io.Serializable
 */
public abstract class ConcurrencyThrottleSupport implements Serializable {

	/**
	 * Permit any number of concurrent invocations: that is, don't throttle concurrency.
	 */
	public static final int UNBOUNDED_CONCURRENCY = -1;

	/**
	 * Switch concurrency 'off': that is, don't allow any concurrent invocations.
	 */
	public static final int NO_CONCURRENCY = 0;
	

	/** Transient to optimize serialization */
	protected transient Log logger = LogFactory.getLog(getClass());

	private transient Object monitor = new Object();

	private int concurrencyLimit = UNBOUNDED_CONCURRENCY;

	private int concurrencyCount = 0;


	/**
	 * Set the maximum number of concurrent access attempts allowed.
	 * -1 indicates unbounded concurrency.
	 * <p>In principle, this limit can be changed at runtime,
	 * although it is generally designed as a config time setting.
	 * <p>NOTE: Do not switch between -1 and any concrete limit at runtime,
	 * as this will lead to inconsistent concurrency counts: A limit
	 * of -1 effectively turns off concurrency counting completely.
	 */
	public void setConcurrencyLimit(int concurrencyLimit) {
		this.concurrencyLimit = concurrencyLimit;
	}

	/**
	 * Return the maximum number of concurrent access attempts allowed.
	 */
	public int getConcurrencyLimit() {
		return this.concurrencyLimit;
	}

	/**
	 * Return whether this throttle is currently active.
	 * @return <code>true if the concurrency limit for this instance is active
	 * @see #getConcurrencyLimit()
	 */
	public boolean isThrottleActive() {
		return (this.concurrencyLimit > 0);
	}


	/**
	 * To be invoked before the main execution logic of concrete subclasses.
	 * <p>This implementation applies the concurrency throttle.
	 * @see #afterAccess() 
	 */
	protected void beforeAccess() {
		if (this.concurrencyLimit == NO_CONCURRENCY) {
			throw new IllegalStateException(
					"Currently no invocations allowed - concurrency limit set to NO_CONCURRENCY");
		}
		if (this.concurrencyLimit > 0) {
			boolean debug = logger.isDebugEnabled();
			synchronized (this.monitor) {
				boolean interrupted = false;
				while (this.concurrencyCount >= this.concurrencyLimit) {
					if (interrupted) {
						throw new IllegalStateException("Thread was interrupted while waiting for invocation access, " +
								"but concurrency limit still does not allow for entering");
					}
					if (debug) {
						logger.debug("Concurrency count " + this.concurrencyCount +
								" has reached limit " + this.concurrencyLimit + " - blocking");
					}
					try {
						this.monitor.wait();
					}
					catch (InterruptedException ex) {
						// Re-interrupt current thread, to allow other threads to react.
						Thread.currentThread().interrupt();
						interrupted = true;
					}
				}
				if (debug) {
					logger.debug("Entering throttle at concurrency count " + this.concurrencyCount);
				}
				this.concurrencyCount++;
			}
		}
	}

	/**
	 * To be invoked after the main execution logic of concrete subclasses.
	 * @see #beforeAccess()
	 */
	protected void afterAccess() {
		if (this.concurrencyLimit >= 0) {
			synchronized (this.monitor) {
				this.concurrencyCount--;
				if (logger.isDebugEnabled()) {
					logger.debug("Returning from throttle at concurrency count " + this.concurrencyCount);
				}
				this.monitor.notify();
			}
		}
	}


	//---------------------------------------------------------------------
	// Serialization support
	//---------------------------------------------------------------------

	private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
		// Rely on default serialization, just initialize state after deserialization.
		ois.defaultReadObject();

		// Initialize transient fields.
		this.logger = LogFactory.getLog(getClass());
		this.monitor = new Object();
	}

}

Other Spring Framework examples (source code examples)

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